Wearable device with capacitive sensor and method of operation therefor

ABSTRACT

A wearable device includes a capacitive sensor and capacitance sensing and calibration logic operative to determine that component drift for a capacitive sensor cannot be determined based on a capacitance sensed by the capacitive sensor. The capacitance sensing and calibration logic deactivates a drift calibration operation for the capacitive sensor while the capacitive sensor senses the capacitance. The capacitance sensing and calibration logic is further operative to determine that the capacitance sensed by the capacitive sensor is within a detection threshold that indicates that a conductive surface is within proximity of the capacitive sensor. The capacitance sensing and calibration logic can also determine that a wearable device, that includes the capacitive sensor, is in motion based on sensed intermittent changes in the capacitance. Various other methods of operation are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure is related to co-pending U.S. patent applicationSer. No. 13/776,103 “CAPACITIVE SENSOR,” which is assigned to the sameassignee as the present application, and which is hereby incorporated byreference herein.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to wearable devices and moreparticularly to capacitive sensors and methods of operation.

BACKGROUND

As mobile devices decrease in size due to continuing advances inminiaturization technologies, some have become “wearable devices” in thesense that these devices may be worn by a user as a fashion accessorysuch as jewelry, an article of clothing, a portion of an article ofclothing, etc. Because of the reduced size of these wearable devices,adding intelligent capabilities becomes challenging due to the limitedspace available for various sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing examples of wearable devices.

FIG. 2 is an axonometric diagram of a wearable device having acapacitive sensor in accordance with an example embodiment.

FIG. 3 is an axonometric diagram of a wearable device having acapacitive sensor in accordance with an example embodiment.

FIG. 4 is one example cross-sectional view of a wearable device similarto that shown in FIG. 2.

FIG. 5 is one example cross-sectional view of a wearable device similarto that shown in FIG. 3.

FIG. 6 is an example cross-sectional view of a wearable device inaccordance with embodiments that are alternative to those shown in FIG.4 and FIG. 5.

FIGS. 7A, 7B and 7C provide example cross-sectional views of variousarrangements that may be used in wearable devices such as those shown inFIG. 2 and FIG. 9.

FIG. 8 is an example assembly diagram of the wearable devices shown inthe cross-sectional views of FIG. 7 such as FIG. 7A.

FIG. 9 is an axonometric diagram of a wristwatch as an example wearabledevice having a capacitive sensor in accordance with an embodiment.

FIG. 10 is an axonometric diagram of a wristwatch as an example wearabledevice having a capacitive sensor in accordance with an embodiment.

FIG. 11 is an axonometric diagram of a wristwatch as an example wearabledevice illustrating positions of capacitive sensor components inaccordance with various embodiments.

FIG. 12 is an axonometric diagram of a wristwatch as an example wearabledevice having a capacitive sensor in accordance with some embodiments.

FIG. 13 is a partial schematic block diagram of a wearable device inaccordance with an example embodiment.

FIG. 14 is a partial schematic block diagram of a wearable mobile devicein accordance with various example embodiments.

FIG. 15 is a partial schematic block diagram of a wearable mobile devicein accordance with various example embodiments.

FIG. 16 is a graph illustrating the usage of sensed capacitance valuesin accordance with various embodiments.

FIG. 17 is a flow chart showing a method of operation in accordance withan embodiment.

FIG. 18 is a flow chart showing a method of operation in accordance withsome embodiments.

FIG. 19 is a flow chart showing a method of operation of a wearabledevice in accordance with some embodiments.

FIG. 20 is a partial schematic block diagram of a capacitive sensor asshown in FIG. 13 (or FIG. 14 or FIG. 15) and in accordance with variousembodiments and shows the variable capacitances seen by the capacitivesensor when a conductive surface comes within proximity.

DETAILED DESCRIPTION

The present disclosure provides methods of operation includingdetermining that component drift for a capacitive sensor cannot bedetermined based on a capacitance sensed by the capacitive sensor, andaccordingly deferring a drift calibration operation for the capacitivesensor while the capacitive sensor senses the capacitance. Thecapacitive sensor may be incorporated into a wearable device andoperatively coupled to capacitance sensing and calibration logic that isoperative to perform various disclosed methods. In one example, thecapacitance sensing and calibration logic is operative to determine thatthe capacitance sensed by the capacitive sensor meets a threshold thatindicates that a conductive surface is within proximity of thecapacitive sensor.

Another disclosed method includes determining that a wearable device,that includes the capacitive sensor, is in motion based on sensedintermittent changes in the capacitance value and reached limits.Various disclosed methods determine when performance of driftcalibration is appropriate. Some methods include sending control signalsto components or applications of a wearable device in response tocertain capacitances sensed by a capacitance sensor or otherconsiderations that are described herein below.

Turning now to the drawings wherein like numerals represent likecomponents, FIG. 1 is a diagram showing example wearable devices 100. Awearable device may include any suitable structure and therefore thepossible wearable devices are not limited to the example wearabledevices 100 shown in FIG. 1. The example wearable devices 100 include amedallion or pendant 109 attached to a lanyard or chain 111, a ring 107,a wristwatch 101 having wristband segments 103 and 105, and a button orbrooch 113 which may include a pin (not shown) for attaching toclothing. Alternatively the button or brooch 113 may be sewn to clothingsuch as a shirt or blouse button, etc. Other example wearable devicesmay include an anklet, a belt buckle, etc.

Axonometric diagrams of wearable devices having a capacitive sensor inaccordance with example embodiments are shown in FIG. 2 and FIG. 3. Theexample embodiments shown in FIG. 2 and FIG. 3 may be implemented as anyof the example wearable devices 100 shown in FIG. 1 or any othersuitable wearable device. In the example embodiment of FIG. 2, awearable device 200 includes a housing 203 and a conductive cover 201which is connected to ground. Although the housings in FIG. 2 and FIG. 3are shown as rectangular for example purposes, it is to be understoodthat the housing of a wearable device may have any suitable shape. Asensor conductor 205 is fitted into a circular cutout portion of thehousing 203 and is isolated from the conductive cover 201 using anon-conductive insulating ring 207 which surrounds the perimeter ofsensor conductor 205 which is likewise circular. The circular shape ofthe sensor conductor 205 is only an example in that the sensor conductor205 may have any of various shapes such as square, rectangular,triangular, octagonal, hexagonal, or some other shape or design. Thesensor conductor 205 and the grounded conductive cover 201 serve asself-capacitance capacitive sensor components and are coupled to othercapacitive sensor components which form circuitry of the capacitivesensor located within the housing 203. That is, a self-capacitancecapacitive sensor senses a capacitance where the sensor conductor formsone “plate” (i.e. one conductive surface) of a capacitor and a secondconductive surface in proximity to the sensor conductor (such as theuser's skin, i.e. a finger, a wrist, etc.) forms the other “plate” ofthe capacitor. The second conductive surface must also be in proximityto ground such that earth ground is coupled to battery ground of thecapacitive sensor in order to complete the circuit.

Another example embodiment is the wearable device 300 shown in FIG. 3.The wearable device 300 also includes a housing 303 and conductive cover301. In the example of FIG. 3, the sensor conductor 305 includes aconductive connection line 307 which extends from the sensor conductor305 to an aperture 309. The aperture 309 is insulated from theconductive cover 301 by way of an insulating grommet 311. The sensorconductor 305 and the conductive connection line 307 are both insulatedfrom the conductive cover 301 by a non-conductive insulating material313 such as an insulating tape. The insulating tape may be, for example,a polyimide material or any other suitable non-conductive insulatingmaterial. The surfaces of the sensor conductor 205, and sensor conductor305 and conductive connection line 307, will also be covered by anon-conductive layer such as, but not limited to, a non-conductivecoating, a non-conductive tape or laminate, etc.

In the examples of both FIG. 2 and FIG. 3, in some embodiments, therespective cover 201 and cover 301 may form part of the respectivehousings and therefore may be considered to be more like a section orportion of the housing rather than a “cover.” That is, a “cover” asdiscussed herein may be removable, or not removable, and may be a halfor other portion of a wearable device housing such that the “cover” maycontain some components of the wearable device (including components ofa capacitive sensor) and the “housing” or other portion of the housingmay contain other components of the wearable device. In other words, a“housing” and “cover” as used herein may be considered to be housingportions, such as first and second housing portions, that form anenclosure that contains the components of a wearable device. Theenclosure may be sealed such that the housing and cover are notseparable, or, the cover may be removable to access internal componentssuch as an internal battery that may be replaceable, a memory card, orsome other component. Put another way, the housing is an enclosure thathas a first portion and a second portion, where one of the first portionor the second portion may be considered to be a cover of the housing orenclosure.

Cross-sectional views of the wearable device 200 and wearable device 300are provided in FIG. 4 and FIG. 5, respectively. The sensor conductor205, which is surrounded by the non-conductive insulating ring 207, maybe press fit or otherwise have an interference fit into a circularcutout portion of the conductive cover 201 to form the cross section asshown in FIG. 4. A non-conductive layer 217 may be applied as a coatingor may be some other suitable non-conductive material. Within thehousing 203, and below the conductive cover 201, is a printed circuitboard (PCB) 209 which may be a flexible circuit board. A connection wire213, or some other suitable connection, forms an electrical connectionbetween the sensor conductor 205 and an appropriate trace line on thePCB surface 211. Although a connection wire 213 is shown in the exampleof FIG. 4, a suitable connection may be formed using other means suchas, but not limited to, a section of flexible PCB, a segment ofconductive tape, a conductive spring, a spring contact such as a springloaded pin contact, or any other suitable type of electrical connection.An air gap may be present between the PCB surface 211 and the bottomsurface of the conductive cover 201 in some embodiments however somenon-conductive insulating material may be present.

When the capacitive sensor is operating, parasitic capacitance willexist between at least the perimeter of the sensor conductor 205 and theconductive cover 201 due to the gap between the sensor conductor 205 andthe conductive cover 201 which is filled by the non-conductiveinsulating ring 207. Additional parasitic capacitance may also existbetween the sensor conductor 205 and trace lines on the PCB surface 211.When a conductive surface 215 comes within proximity of the sensorconductor 205, or in contact with the surface of the non-conductivelayer 217, an additional capacitance is formed between the conductivesurface 215 and the sensor conductor 205 thereby affecting the overallcapacitance seen by the capacitive sensor. The conductive surface 215may only come within proximal distance of the sensor conductor 205 andconductive cover 201 or may come into contact with the surface ofnon-conductive layer 217 to produce various capacitance values sensed bythe capacitive sensor.

The cross-sectional view of the wearable device 300 illustrated in FIG.5 shows the sensor conductor 305 and the conductive connection line 307positioned on top of the non-conductive insulating material 313. Asdiscussed above, the non-conductive insulating material 313 may be anysuitable non-conductive insulating material such as a polymer and maybea polyimide such as a polyimide tape or laminate. The sensor conductor305 and the conductive connection line 307 are also covered bynon-conductive material segments 325 and 323, respectively, which mayalso be formed from a polyimide tape or laminate or may be anon-conductive coating material. In some embodiments, the non-conductivecovering material, which may be a coating, may cover the entire surfaceof the conductive cover 301 including the sensor conductor 305 andconductive connection line 307. The conductive connection line 307extends from the sensor conductor 305 up to some suitable position abovethe aperture 309 so that the conductive connection line 307 eithercontinues through the aperture 309 or is further connected, by forexample connection wire 319, to an appropriate trace on the PCB surface317 of PCB 315. The connection wire 319 may either be an extension ofthe conductive connection line 307, a segment of conductive tape, aflexible connection line or piece of flexible PCB, a conductive spring,a spring contact such as a spring loaded pin contact, or any othersuitable type of electrical connection. The conductive cover 301 isconnected to circuit ground within the housing 303. Similar to theexample illustrated in FIG. 4, and air gap may exist between the bottomsurface of the conductive cover 301 and PCB surface 317, oralternatively, some non-conductive insulating material may be present.The capacitive sensor again may be actuated by a conductive surface 321coming within a proximal distance of the sensor conductor 305 andconductive cover 301, or into contact with one or both of thenon-conductive material segments 323 and 325. The conductive surface 321may also come into full contact with the surface of a non-conductivelayer or coating that covers the entirety of the sensor conductor 305and conductive cover 301 as was discussed above.

Another example embodiment is illustrated by the cross-section ofwearable device 400 shown in FIG. 6. The wearable device 400 includes amulti-layer PCB 405 which may be a double-sided PCB or some other typeof multi-layer PCB, which may be a flexible PCB, and which is positionedwithin the housing 403. A sensor conductor 407, which may be circular orsome other shape, is formed as a conductive trace on the PCB surface 413of multi-layer PCB 405. On the opposite side of a non-conductive layer409 is a shield 411 which is formed by a conductive plane such as acopper plane. The shield 411 is a driven shield which is driven to thesame potential as the sensor conductor 407 to protect against couplingor interference with any circuit or other components physically locatedbelow the multi-layer PCB 405 within the housing 403. A non-conductivecover 401 is situated above the multi-layer PCB 405 and may also be acover of the housing 403. The non-conductive cover 401 may be formedfrom any suitable non-conductive material such as, but not limited to, athermoplastic polymer and may be a polycarbonate material in someembodiments. The bottom surface of the non-conductive cover 401 maydirectly contact the sensor conductor 407 surface or an air gap may bepresent in some embodiments. The capacitive sensor is activated when aconductive surface 415 comes within a proximal distance of, or incontact with, the top surface of the non-conductive cover 401 such thata capacitance is formed between the conductive surface 415 and thesensor conductor 407. The sensor conductor 407 may be suitably coupledto other capacitive sensor components by trace lines on the PCB surface413 and/or by PCB via (not shown) penetrating the layers of themulti-layer PCB 405 to couple with other capacitive sensor componentsforming the capacitive sensor circuitry located within the housing 403.

Other example embodiments are illustrated in FIGS. 7A, 7B and 7C by thecross-sectional views of respective wearable devices 700, 730 and 760.An example assembly view is also provided in FIG. 8, to shown furtherexample details of the wearable device 700 shown in FIG. 7A. In FIG. 7Aand FIG. 8, a non-conductive, decorative medallion 705 is fitted into acutout or bore 801 of a conductive cover 701 that covers a housing 703of wearable device 700. The decorative medallion 705 is “decorative” inthat it may include a design on its surface such as, but not limited to,a company logo, a user's initials, or some other design, etc. In theexample of FIG. 7A, the decorative medallion 705 is secured into thecutout or bore 801 using a non-conductive, insulating grommet 707 and anadhesive 717 which forms an adhesive layer that secures the decorativemedallion 705 to the PCB surface 713. The PCB 711 may be a flexible PCBand may be a single layer or multi-layer PCB in the various embodiments.The adhesive is non-conductive and may be an epoxy, such as an epoxyresin or some other suitable non-conductive adhesive formulation, or maybe a non-conductive adhesive tape. One example of a non-conductiveadhesive tape may be a double coated tape with a pressure sensitiveadhesive on one side and an acrylic adhesive on the other side. In someembodiments, the tape may be formed using a polyester film carrier andhave the coatings described above.

The insulating grommet 707 has a T-shaped cross-section as shown and hasan appropriate shape so that it surrounds the perimeter of thedecorative medallion 705. For example, the insulating grommet 707 may becircular for embodiments in which the cutout or bore 801 and decorativemedallion 705 are circular. However, the insulating grommet 707 may beany suitable shape such as, but not limited to, oval, triangular,rectangular, square, hexagonal, octagonal, or some other shape etc. soas to fit, and provide electrical insulation and a water seal for,like-shaped decorative medallions. That is, the decorative medallion 705may also be any shape. The example insulating grommet 707 includes anaxially extending cylindrical portion 708 that extends from a radialdisc portion 712. The axially extending cylindrical portion 708 has aninner diameter suitable to form an interference fit with the outerdiameter of the decorative medallion 705. The outer diameter of theaxially extending cylindrical portion 708 inserts into the cutout orbore 801 and is sized to form an interference fit therewith. A bottomsurface of the radial disc portion 712 is seated on the PCB surface 713and may also be secured using an adhesive. The radial disc portion 712includes a radially inwardly extending portion 709 on which thedecorative medallion 705 is seated and which forms a water tight seal,along with adhesive 717, between the decorative medallion 705 and thePCB 711. The conductive cover 701 is seated on a radially outwardlyextending portion 710 which also forms a water tight seal, along withadhesive 719, between the conductive cover 701 and the PCB 711.

The adhesive 719 surrounds at least the outer perimeter of the radiallyoutwardly extending portion 710 and forms an adhesive layer between thebottom surface of the conductive cover 701 and the PCB surface 713, andhelps secure the conductive cover 701 to the PCB surface 713. Theadhesive layer formed by adhesive 717 and the adhesive layer formed byadhesive 719 are coplanar, and may be separated only by a portion of thegrommet 707 that contacts the same respective surfaces. That is, theadhesive 717 fills the circular area formed by the inner circumferenceof the radially inwardly extending portion 709 and forms an adhesivelayer between the bottom surface of the decorative medallion 705 and thePCB surface 713, and also helps secure the decorative medallion 705 tothe PCB surface 713. As mentioned above, the insulating grommet 707,along with the adhesive layers formed by adhesives 717 and 719, formwater tight seals that prevent water or other liquids from seepingaround the cutout or bore 801 and getting onto the PCB surface 713 orinto the housing 703. The insulating grommet 707 may be formed from asuitable elastomeric material such as a suitable synthetic rubber andmay be flexible material. The adhesives 717 and 719 may be the sameadhesives, that is, an epoxy, such as an epoxy resin or some othersuitable non-conductive adhesive formulation as discussed above.

A sensor conductor 715 is positioned on the PCB surface 713, beneath thedecorative medallion 705, and may also be covered by the adhesive 717.The sensor conductor 715 may be circular as shown in the example of FIG.8, and is formed from copper conductor on the PCB surface 713. In otherexamples, the sensor conductor 715 may be any shape such as, but notlimited to, oval, triangular, rectangular, square, hexagonal, octagonal,or some other shape etc. The sensor conductor 715 may be coupled toother circuitry using copper trace lines along the PCB surface 713,and/or by via running through one or more layers of the PCB 711.

The cross-sectional views of FIGS. 7B and 7C illustrate examples that donot use the insulating grommet 707. In FIG. 7B the wearable device 730includes a decorative medallion 735 fitted into a cutout or bore of aconductive cover 731 with an interference fit 737 between the perimeterof the decorative medallion 735 and the inner surface or the conductivecover 731 cutout or bore. The conductive cover 731 covers a housing 733which contains PCB 741 which may be a flexible PCB and may have one ormore layers. The PCB surface 743 of PCB 741 includes a sensor conductor745 which may have any shape. The decorative medallion 735 is secured tothe PCB surface 743 by an adhesive layer formed by adhesive 747 whichmay cover the surface of sensor conductor 745. The cover 731 is alsosecured to the PCB surface 743 by adhesive 749 which forms an adhesivelayer that is coplanar with the adhesive layer formed by adhesive 747. Atolerance gap 739 may be present between the adhesive layers formed byadhesives 749 and 747 to allow for expansion of the adhesives due to,for example, temperature or pressure, or other conditions. The adhesives747 and 749 are the same type as discussed for FIG. 7A above.

The example wearable device 760 shown in FIG. 7C has the same featuresas the wearable device 730 and therefore includes a decorative medallion765 fitted into a cutout or bore of a conductive cover 761 with aninterference fit 767 between the perimeter of the decorative medallion765 and the inner surface or the conductive cover 731 cutout or bore.Adhesive 777 secures the decorative medallion 765 to the PCB surface 773of PCB 771. In this example, PCB 771 is a multi-layer flexible PCB andincludes a shield 783 which is formed by a conductive layer on a PCBsurface opposite the sensor conductor 775. Like the example provide inFIG. 6, the shield 783 is a driven shield which is driven to the samepotential as the sensor conductor 775 to protect against coupling orinterference with any circuit or other components physically locatedbelow the multi-layer PCB 771 within the housing 763. Adhesive 779secures the conductive cover 761 to the multi-layer PCB 771 to cover thehousing 763 and forms an adhesive layer that is coplanar to the adhesivelayer formed by adhesive 777. A tolerance gap 769 may be present betweenthe adhesive layers formed by adhesives 777 and 779 to allow forexpansion of the adhesives due to, for example, temperature or pressure,or other conditions. The adhesives shown in both FIG. 7B and FIG. 7Cform watertight seals between the respective conductive covers and PCBsurfaces to prevent water or other liquid or debris from contaminatingthe PCB surfaces 743, 773 or from getting into the housings 733, 763.The watertight seal is achieved in the examples of FIG. 7B and FIG. 7Cwithout the need for the grommet 707 shown in the FIG. 7A example. Theadhesives 777 and 779 are the same type as discussed for FIG. 7A andFIG. 7B above.

In operation of any of the configurations shown in FIG. 7A, 7B or 7C, acapacitance change is sensed by the respective capacitive sensors whenthe conductive surface 723 comes within proximity of the sensorconductors 715, 745, 775, or into contact with the surface of thenon-conductive decorative medallions 705, 735 or 765. The decorativemedallions described above may be considered to be a “section” of theconductive covers, or, in other words, a section of a portion of thewearable device housing. Put another way, the wearable device housingshave a first portion that houses a PCB with a sensor conductor, and asecond portion that has a conductive section and a non-conductivesection. The conductive section of the second portion (such as thecover) is connected to ground. The non-conductive section of the secondportion is the decorative medallion which is positioned above or overthe sensor conductor on the PCB. The perimeter of the decorativemedallion is larger than the perimeter of the sensor conductor such thatthe sensor conductor perimeter would fit within the perimeter of thedecorative medallion.

It is to be understood that the cross-sectional views provided in FIG.4, FIG. 5, FIG. 6, FIGS. 7A, 7B, and 7C and described herein, areexamples only for purposes of describing the arrangement of componentsrelative to one another and are not to scale and illustrate certaincomponents such as the various PCBs in a simplified manner. That is, thevarious PCBs depicted may consist of multiple layers not shown such as,for example, coverlays formed from polyimide or other suitablenon-conductive materials, various adhesive layers, conductive tracelayers and sections, various non-conductive layers, via for connectingpoints on various layers, etc., and such other layers, via, etc., notshown, but where necessary, are understood to be present by those ofordinary skill. Also, the assembly view of FIG. 8 is likewise an examplefor the purpose of description of components relative to one another, aswell as describing some features of the components, and is not to scale.

Some example dimensions will now be provided for an example embodimentrelated to FIG. 7 and FIG. 8. However, it is to be understood that thesedimensions are examples only that are not to be construed as limiting orrequirements and that, in light of the disclosure and descriptionprovide herein, such dimensions may be modified by those of ordinaryskill to arrive at various other contemplated embodiments that havedifferent dimensions and different parasitic capacitances and that suchother embodiments are contemplated by the inventors in disclosing suchexample dimensions. That is, the example dimensions provided areapproximate in that they are not only to be understood as being withinsome mechanical tolerance suitable for the example embodiment, but alsomay be modified in relation to other components by increased or reducedvalues that retain the features and functions described herein ascontemplated by the disclosed embodiments. Example dimensions in oneexample embodiment include a distance 721 from the perimeter edge of thesensor conductor 715 to the edge of the internal surface of the cutoutor bore 801 of the conductive cover 701. An example distance 721 may beapproximately 1.0 mm. Likewise, the distances 751 and 781 may beapproximately 1.0 mm. The adhesive layers formed by adhesives 717 and719 may be approximately 0.05 mm thick between the PCB surface 713 andthe bottom surfaces of the decorative medallion and the conductive cover701, respectively. The conductive cover 701 may have an approximatethickness of 0.3 mm. The decorative medallion 705 may be circular asshown in FIG. 8, but is not limited to being circular, and may have adiameter of approximately 12 mm and a thickness of 0.3 mm. The sensorconductor 715 may be circular and may have a diameter of approximately10 mm. The PCB 711, which may be a flexible PCB, may have a thickness ofapproximately 0.1 mm or thicker depending on the number of layersincorporated in the PCB 711. For example, multi-layer PCB 771 whichincludes shield 783 will be thicker than PCB 711 due to having theadditional layer to form shield 783. With respect to the insulatinggrommet 707, the axially extending cylindrical portion 708 that extendsfrom the radial disc portion 712 as measured from the connected surfaceof the radial disc portion 712, may have a height of approximately 0.3mm to match the respective thicknesses of the decorative medallion 705and the conductive cover 701 as illustrated in the cross-sectional viewof FIG. 7. Other relative thicknesses and distances may be used in otherembodiments that result in different parasitic capacitances between thevarious components and that may affect the baseline, untouchedcapacitance value of the sensor accordingly and any such embodiments arecontemplated by the present disclosure. In operation, as a conductivesurface 723 gets near to the outer surfaces of the conductive cover 701and the decorative medallion 705, or like components in FIG. 7B and FIG.7C, a capacitance change, from an “untouched” standalone capacitancewill be sensed using the sensor conductor 715 or sensor conductors 745and 775 in FIG. 7B and FIG. 7C, respectively.

The example assembly view of FIG. 8 also shows that a shield 803 mayalso be included and is larger than the perimeter of the sensorconductor 715. In the FIG. 8 example, the shield 803 is circular with adiameter larger than the diameter of circular sensor conductor 715.However, the shield may form a layer that covers an entire surface ofthe PCB 711 in some embodiments.

Various additional example embodiments are provided in FIG. 9, FIG. 10,FIG. 11 and FIG. 12. The example embodiment shown in FIG. 9 may employany of the capacitive sensor configurations shown and described in FIG.4, FIG. 6, FIGS. 7A, 7B, 7C and FIG. 8. A wristwatch 900 includes twowristband segments 907 and 909 which are attached to a housing 905 andwhich include a conductive cover 901 which is grounded. In someembodiments, a circular sensor conductor 903 is positioned within acorresponding circular cut-out or bore of the conductive cover 901 andis insulated by a non-conductive insulating ring or grommet 911. When auser places the wristwatch 900 on the user's wrist, and fastens thewristband segment 907 to wristband segment 909, the sensor conductor 903will sense capacitance due to the user's wrist (which acts as aconductive surface) and will thereby detect that the wristwatch 900 isin use. In other embodiments, the sensor conductor 903 may be located ona PCB beneath the conductive cover 901 such that the sensor conductor903 is not visible. In such embodiments, a non-conductive, decorativemedallion, which may be circular, or some other shape, may be fittedwithin the cutout as was described with respect to FIGS. 7A, 7B and 7C.In FIG. 10, an example wristwatch 1000 includes a sensor conductor 1003positioned on a conductive cover 1001 along with a conductive extensionline 1011. The conductive extension line 1011 connects the sensorconductor to capacitive sensor components within the housing 1005 usingan aperture 1013 which is insulated by an insulating grommet 1015. Theconductive extension line 1011 is electrically connected through theaperture 1013 to other capacitive sensor components that form thecapacitive sensor circuitry located within the housing 1005. Thecross-sectional view shown in FIG. 5 is an example of a configurationthat may be used in conjunction with the example wristwatch 1000 shownin FIG. 10. When the wristwatch 1000 user fastens the wristband segment1007 with the wristband segment 1009 around the user's wrist, the sensorconductor 1003 will form a capacitance with the user's wrist as aconductive surface, and the capacitive sensor will sense a change incapacitance indicating that the wristwatch 1000 is in use. The sensorconductor 1003 and the conductive extension line 1011 are insulated fromthe grounded conductive cover 1001 via non-conductive insulatingmaterial 1017 and are insulated from the user's wrist via a similarnon-conductive insulating material or by a non-conductive coating.

FIG. 11 and FIG. 12 provide additional examples for how the sensorconductor and ground conductor may be configured and positioned inembodiments related to an example wristwatch 1100 and an examplewristwatch 1200, respectively. In the example of FIG. 11, variousoptional possible conductor positions are illustrated by dotted lines.For example, conductor 1103 may be located within a cutout or bore ofthe cover 1101 which may be a conductive cover in some embodiments. Thecover 1101 covers a housing 1105. In another embodiment, the conductor1103 may be located beneath the cover 1101 such that it is not visibleto the user. Examples of such configurations are provided in FIGS. 6,7A, 7B and 7C which are described in detail above. For example, as shownin FIG. 7A and FIG. 8, the conductor is located beneath anon-conductive, decorative medallion. In embodiments where the cover1101 is conductive, and where the conductor 1103 is located eitherembedded in or on top of the cover 1101, an appropriate insulator 1111may be used to isolate the conductor 1103. A wristband conductor 1113positioned on wristband segment 1107, or a wristband conductor 1115positioned on wristband segment 1109, may also be used in someembodiments. That is, any one of conductor 1103, wristband conductor1113 or wristband conductor 1115 may be used as a sensor conductor whileone of the other conductors serves as a ground conductor. For example,conductor 1103 may be used as a sensor conductor and wristband conductor1113 or wristband conductor 1115 may be used as a ground conductor.Alternatively, one of the wristband conductors 1113 or 1115 may be usedas the sensor conductor and the conductor 1103 may be used as the groundconductor. In some embodiments, one of the wristband conductors 1113 or1115 may be used as the sensor conductor with the other wristbandconductor being used as the ground conductor. In yet another alternativeembodiment example, one of the wristband conductors 1113 or 1115 may beused as a sensor conductor while the cover 1101, if conductive, may beused as a ground conductor. Therefore it is to be understood thatvarious combinations of the optional conductor positions illustrated inFIG. 11 may be arranged so as to implement a sensor conductor and aground conductor for purposes of creating a self-capacitance capacitivesensor. Also, in other embodiments, any two of the optional conductorlocations shown in FIG. 11 may be used to create a mutual capacitancecapacitive sensor with one conductor serving as transmit conductor andanother conductor serving as a receive conductor.

The example wristwatch 1200 shown in FIG. 12 includes the housing 1205which has a wristband segment 1207 and a wristband segment 1209 attachedand a cover 1201 which covers the housing 1205. In the example of FIG.12, cover 1201 is divided into a first section 1211 and a second section1213 divided as shown by the demarcation line 1203 which is forillustrative purposes only. The first section 1211 and the secondsection 1213 may both be conductive sections. However, in someembodiments, one section may be conductive and the other section may benon-conductive. In this case, a sensor conductor may be located beneaththe non-conductive section and the conductive section may be grounded tocreate a self-capacitance sensor scheme. In other embodiments, whereboth sections are conductive, a self-capacitance capacitive sensorscheme may be created by using one of the first or second sections 1211or 1213 as the sensor conductor and using the other of the twoconductive sections as a ground conductor accordingly. The configurationillustrated in FIG. 12 may also be used in some embodiments to implementa mutual capacitance capacitive sensor scheme with one side as atransmit conductor and the other as a receive conductor. In yet otherembodiments, a mutual capacitance grid may be formed by dividing thesurface of the cover 1201 into many sections (i.e. more than two) toform multiple transmit and receive sections such as in a grid.Alternatively, the PCB may be routed to form such a grid, similar to amobile phone touch screen.

FIG. 13, FIG. 14 and FIG. 15 are partial schematic block diagrams ofwearable devices that are examples of apparatuses in accordance withvarious embodiments. FIG. 13, FIG. 14 and FIG. 15 provide examples ofwearable devices for the purpose of describing to those of ordinaryskill how to make and use the disclosed subject matter by way of variousembodiments. FIG. 20 is a partial schematic block diagram that providesfurther details of a capacitive sensor shown in FIG. 13 in accordancewith various embodiments. It is to be understood that FIG. 13, FIG. 14,FIG. 15 and FIG. 20 are partial schematic block diagrams in that,although the diagrams show at least those components necessary todescribe the features and advantages of the various embodiments to thoseof ordinary skill, various other components, circuitry, and devices maybe necessary in order to implement a complete functional apparatus suchas the example wearable devices and that those various other components,circuitry, devices, etc., are understood to be present by those ofordinary skill.

FIG. 13 illustrates a wearable device 1300 having a capacitive sensor1301 and capacitance sensing and calibration logic 1320 operativelycoupled via connection path 1303. That is, there may be one or moreintermediate or intervening components between, or along the connectionpath 1303 such that the capacitive sensor 1301 and the capacitancesensing and calibration logic 1320 are understood to be operativelycoupled. The partial schematic block diagram of FIG. 13 is applicable toany of the various embodiments having physical configurations similar tothose illustrated in FIG. 2, FIG. 3, or to the cross-sectional viewsshown in FIG. 4, FIG. 5, FIG. 6 or FIG. 7A, 7B, 7C. The capacitivesensor 1301 drives the capacitance sensing and calibration logic 1320along the connection path 1303 in response to a conductive surfaceplaced within proximity of the capacitive sensor 1301. A conductivesurface may be, for example, a user's finger, wrist, or some otherportion of the user's skin serving as the conductive surface, an articleof clothing, or a patch of conductive material that is either includedwithin or attached to an article of clothing. In response to changes incapacitance sensed by the capacitive sensor 1301, the capacitancesensing and calibration logic 1320 may make various determinations. Forexample, the capacitance sensing and calibration logic 1320 maydetermine whether the user is wearing a wearable device 1300, whetherthe user wearing the wearable device 1300 is in motion, and possiblywhether the user is wearing the wearable device 1300 loosely or tightlybased on when the wearable device 1300 comes into proximity or makesintermittent contact with a conductive surface such as the user's wrist.The capacitance sensing and calibration logic 1320 may includecomponents such as wear detection logic 1321, motion detection logic1325 and drift calibration logic 1323. These components may interact andcommunicate with one another as needed to accomplish their respectivefunctions. For example, the wear detection logic 1321 may providecontrol signaling to the drift calibration logic 1323 to defer driftcalibration procedures under appropriate conditions determined by thewear detection logic 1321. Likewise the wear detection logic 1321 maycommunicate and receive information from the motion detection logic1325. In some embodiments, the wear detection logic 1321 and motiondetection logic 1325 may be integrated into a single component. Forexample, the wear detection logic 1321 may determine that the user iswearing the wearable device 1300 and the motion detection logic 1325 maydetermine that the user is also in motion. Under such circumstances, thewear detection logic 1321 may send a control signal to the driftcalibration logic 1323 to defer drift calibration if the user is wearingthe wearable device 1300 loosely. This may be accomplished in variousways such as, but not limited to, deactivating the drift calibrationlogic 1323, or by placing the drift calibration logic 1323 into asuspended mode or sleep mode or by imposing a wait state in which thedrift calibration logic 1323 waits for further instructions beforecommencing further activity. The wear detection logic 1321 may also senda control signal to the drift calibration logic 1323 to start driftcalibration as soon as the user is determined by the wear detectionlogic 1321 to be not in proximity with the sensor such as when thewearable device 1300 is loosely worn and somewhat away from the user(i.e. the conductive surface) for an extended period of time such as fora number of seconds. The motion detection logic 1325 may assess motionfrom the capacitance profile behavior such as by using capacitancevalues, timing, fluctuations, peaks and lows, limits, etc. These methodsof operation are described in further detail with respect to variousother drawings provided herein.

The capacitance sensing and calibration logic 1320 or any of itscomponent logic may be implemented independently as software and/orfirmware executing on one or more programmable processors (includingCPUs and/or GPUs), and may also include, or may be implementedindependently, using ASICs, DSPs, hardwired circuitry (logic circuitry),or combinations thereof. That is, the capacitance sensing andcalibration logic 1320 may be implemented using an ASIC, DSP, executablecode executing on a processor, logic circuitry, or combinations thereof.Further example details of a capacitive sensor 1301 are provide in FIG.20 which is described below, after a discussion of various structuresthat may be used in the various embodiments to obtain a sensor conductorand a ground conductor in a wearable device. That is, FIG. 20 is bestunderstood in relation to the various possible structures that may beused in the various embodiments.

The partial schematic diagram of FIG. 14 illustrates various examples ofhow the entire capacitive sensor, or capacitive sensor components insome embodiments, may be positioned on a wearable device 1400. That is,the partial schematic diagram of FIG. 14 illustrates possible electricalconfigurations that may be used in example embodiments having physicalconfigurations such as the wristwatch 900 illustrated in FIG. 9, thewristwatch 1000 illustrated in FIG. 10, the wristwatch 1100 illustratedin FIG. 11 or the wristwatch 1200 illustrated in FIG. 12. Therefore inFIG. 14, various blocks (capacitive sensor 1401, 1433, 1443; connectors1403, 1405, 1431, 1441, 1435, 1445) are shown having dotted lines toillustrate that various physical positions may be selected for thecapacitive sensor or distributions of the capacitive sensor components.A “capacitive sensor component” refers to the sensor conductor, thesensor ground conductor, any shield, and capacitive sensor circuitcomponents including a PCB. That is, the “capacitive sensor” blocksshown as dotted line blocks in FIG. 14 may refer to positions of some,or all, “capacitive sensor components” in embodiments where theconductive components are placed, for example, with one conductor on awristband and another on the wearable device housing; both conductors ona single wristband; one conductor on each wristband, etc. Furthermore,in addition to the above example combinations being used to implementself-capacitance schemes, the conductor combinations may alternativelybe used as transmit and receive sensor locations for mutual capacitanceimplementations in some embodiments. A complete “capacitive sensor” asused herein refers to the set of “capacitive sensor components” requiredto implement the “capacitive sensor.” Examples of the “capacitive sensorcomponents” include, but are not limited to, the sensor conductor,ground conductor, shield conductors, oscillators, comparators, clockingcircuits, operational amplifiers, other active components such astransistors, and passive components such as, but not limited to, thecapacitors that may be formed by the sensor conductor and groundconductors all of which are understood to be present by those ofordinary skill for implementing self-capacitance or mutual capacitancecapacitive sensors. In some embodiments, some of the capacitive sensorcomponents may be integrated into, or provided by, the capacitancesensing and calibration logic 1420.

In one example, capacitive sensor 1401 (including all capacitive sensorcomponents) may be physically positioned on or within the housing of thewearable device 1400 as shown in the various example configurations ofFIG. 2, FIG. 3, FIG. 9 through FIG. 12 and the cross-sectional views ofFIG. 4 through FIG. 7. Similar to the examples described with respect toFIG. 11, the capacitive sensors 1433 and 1443 may be located onwristbands 1430 or 1440, respectively. For example, the capacitivesensor 1433 may be the capacitive sensor for the wearable device 1400and may be coupled to connector 1431 of the wristband 1430 using aflexible connection 1435. The connector 1431, is coupled to thecapacitive sensor 1433 and is also coupled to the housing of thewearable device 1400 by connector 1403. The combination of connector1403 and connector 1431 may also be flexible such that flexing of thewristband 1430 does not damage or disconnect the operative connectionbetween the capacitive sensor 1433 and the connection bus 1407 which isconnected to connector 1403.

The wristband 1440 illustrates a similar configuration with theconnection bus 1407 connected to connector 1405. The connector 1405 isattached to the wearable device 1400 housing and couples to connector1441 and capacitive sensor 1443 which is coupled to the connector 1441via flexible connection 1445.

Therefore in some embodiments, the example wearable device 1400 may haveelectrical capacitive sensor component configurations according to thephysical configuration used such as the example physical configurationsthat have been described with respect to the wristwatch 1100 in FIG. 11.In other words, any one of the possible conductive component locationsshown in FIG. 11 may be used to form a capacitive sensor scheme.Likewise, FIG. 14 illustrates example internal connections for acapacitive sensor that may be arranged corresponding to the possiblelocations shown for capacitive sensor 1401, 1433, or 1443, where oneconductor serves as a sensor conductor and another serves as a groundconductor to complete the circuit required to implement aself-capacitance capacitive sensor, or alternatively, a mutualcapacitance sensor. That is, FIG. 14 is for the purpose of showing thatthe capacitive sensor in accordance with various embodiments may beimplemented using conductive components located either on, or embeddedinto, a surface of the wearable device 1400 housing or housing cover,within the wearable device 1400 housing, on one or both wristbandsconnected to the wearable device 1400 housing or some combinationthereof so that one conductive component provides the sensing componentwhile the other serves as a ground conductor (or alternatively, as atransmit conductor and a receive conductor). A conductive cover for thehousing may also be used as a ground conductor as described abovepreviously.

Similar to the embodiment illustrated in FIG. 13 the wearable device1400 also includes capacitive sensing and calibration logic 1420operatively coupled to the capacitive sensor by a connection bus 1407.The capacitance sensing and calibration logic 1420 may be a singleintegrated logic component or may include wear detection logic 1421,motion detection logic 1425 and drift calibration logic 1423 which mayalso be operatively coupled to each other to communicate with each otheras was described with respect to the embodiment of FIG. 13. Forembodiments where the capacitive sensor is implemented in eitherwristband 1430 or wristband 1440, the capacitance sensing andcalibration logic 1420 is operatively coupled to the wristbandcapacitive sensors accordingly by one or both of the connectors 1403 or1405 and connection bus 1407.

Partial schematic block diagram of FIG. 15 illustrates an exampleembodiment of a wearable device 1500 where the capacitance sensing andcalibration logic 1550 is implemented as executable code 1504 executedby a processor 1501. The executable code 1504 corresponding to thecapacitance sensing and calibration logic 1550 may be stored innon-volatile, non-transitory memory such as memory 1503, and read frommemory 1503 as needed for execution by processor 1501. The capacitancesensing and calibration logic 1550 may include wear detection logic1551, drift calibration logic 1553 and motion detection logic 1555. Eachof these components also have corresponding executable code within theexecutable code 1504 and such executable code is also executed by theprocessor 1501 in accordance with the example embodiment of FIG. 15. Thecapacitance sensing and calibration logic 1550 may also communicate andinteract with one or more applications 1511 which are also executed bythe processor 1501, or other components of wearable device 1500. Suchapplications may also be stored as executable code (not shown) in memory1503.

The wearable device 1500 is an apparatus in accordance with anembodiment and includes connection bus 1505 to provide operativecoupling between various components including the at least one processor1501, memory 1503, network transceiver 1507, peer-to-peer transceiver1509, display/UI 1513, other UI 1515, connectors 1519 and 1521 whenpresent, and capacitive sensor 1517 when present within the housing ofwearable device 1500, etc. The connection bus 1505 provides operativecoupling in that various intermediate or intervening wearable device1500 components, circuitry, and the like, may exist in between, and/oralong, the communication path between any two or more operativelycoupled components, etc. The wearable device 1500 may have two wristbandsegments 1530 and 1540 connected to the wearable device 1500 housing.One or both of the wristband segments 1530 and 1540 may includeconnectors 1531 and 1541, respectively, which may be flexibleconnectors. One or more capacitive sensor components, or the entirecapacitive sensor, may be located within one of the wristband segments.These possible locations are illustrated by blocks shown having dottedlines in FIG. 15 such as capacitive sensor 1517 and capacitive sensors1533 and 1543 which correspond to the wristband segments 1530 and 1540,respectively. Either of the capacitive sensors 1533 or 1543 when presentmay also have a corresponding flexible connection 1535 or 1545,respectively. In other words, the wearable device 1500 may have aphysical configuration for a capacitive sensor using various placementsof the capacitive sensor components according to any one of the variousexamples described with respect to FIG. 11.

It is to be understood that FIG. 15 illustrates examples of componentsthat may be present in a wearable device 1500 and that one or more ofthe various components shown in FIG. 15, other than the capacitivesensor and capacitance sensing and calibration logic 1550, may beomitted from the wearable device 1500 without detracting from enjoymentof the benefits, features and advantages of the present disclosure. Thatis, different wearable devices may or may not include some of theexample components shown in FIG. 15 and therefore none of these examplecomponents are to be construed as being required for any particularembodiment.

The display/UI 1513, if present, may provide a touchscreen userinterface and, in some embodiments, may also provide a graphical userinterface (GUI). The network transceiver 1507, if present, may providewireless communication capabilities for one or more wide area networkcommunications systems such as, but not limited to, Wi-Fi cellular, 2G,3G or 4G wireless communications systems. The peer-to-peer transceiver1509, if present, may provide wireless connectivity capabilities suchas, but not limited to, Bluetooth™, Wireless USB, ZigBee, or othertechnologies, etc. such as near field communication (NFC). The other UI1515, if present, may include a track ball mouse, touch sensitiveelements, physical switches, gyroscopic position sensors, etc. Thedisplay/UI 1513, if present, may include touchscreen functionality asnoted above, and may be operative to receive command and control signalsfrom the other UI 1515 directly, or via the processor 1501, forfunctions such as, but not limited to, mouse cursor control click toprovide selection input and or drag and drop features or otherfunctionality in some embodiments.

The memory 1503 is a non-volatile, non-transitory memory, and stores theexecutable code 1504 corresponding to the capacitance sensing andcalibration logic 1550 including any component logic such as the weardetection logic 1551, motion detection logic 1555 or drift calibrationlogic 1553. The processor 1501 is operative to execute the executablecode 1504, which may be stored in memory 1503, to perform the methods ofoperation disclosed herein.

The various embodiments also include non-volatile, non-transitorycomputer readable memory, other than memory 1503, that may containexecutable instructions or executable code, for execution by at leastone processor, that when executed, cause the at least one processor tooperate in accordance with the functionality and methods of operationherein described. The computer readable memory may be any suitablenon-volatile, non-transitory, memory such as, but not limited to,programmable chips such as EEPROMS, flash ROM (thumb drives), compactdiscs (CDs) digital video disks (DVDs), etc., that may be used to loadexecutable instructions or program code to other processing devices suchas wearable devices or other devices such as those that may benefit fromthe features of the herein described embodiments.

The operation of the capacitance sensing and calibration logic 1550shown in FIG. 15, (also capacitance sensing and calibration logic 1320shown in FIG. 13 and capacitance sensing and calibration logic 1420shown in FIG. 14) is best understood in conjunction with FIG. 16, FIG.17, FIG. 18 and FIG. 19, which will now be described. FIG. 16 is asensed capacitance graph 1600 illustrating the usage of sensedcapacitance values sensed by a capacitive sensor in accordance withvarious embodiments described above. FIG. 17, FIG. 18 and FIG. 19 areflow charts showing methods of operation in accordance with variousembodiments.

For purposes of simplifying explanation and also for clarity, thefollowing description will refer to the capacitance sensing andcalibration logic 1550 and the capacitive sensor 1517 shown in FIG. 15.However it is to be understood that the present explanation appliesequally to the capacitance sensing and calibration logic 1320 andcapacitive sensor 1301 shown in FIG. 13 and to the capacitance sensingand calibration logic 1420 and the applicable capacitive sensor(selected from capacitive sensor 1401, 1433, or 1443, or somecombination thereof). Referring to FIG. 16, the sensed capacitance graph1600 illustrates that the capacitive sensor 1517 will exhibit astandalone capacitance “C_(standalone)” 1601 which is a baselinecapacitance value determined for the capacitive sensor in the factoryduring production. As understood by those of ordinary skill, thebaseline capacitance C_(standalone) may exhibit a capacitance change1603 over some percentage range above or below the baseline valueC_(standalone) due to component drift caused by temperature variations,component aging, etc. A detection threshold capacitance,“C_(detection threshold)” 1605, is used to determine when a conductivesurface comes within a proximity of the capacitive sensor. The detectionthreshold capacitance C_(detection threshold) 1605 may at times beaffected adversely by the capacitance change 1603. However driftcompensation and calibration operations adjust the baseline capacitancevalue such that the capacitance C_(detection threshold) 1605 ismaintained at an appropriate level above the C_(standalone) 1601 todiscern a change in capacitance caused by a proximal conductive surfacefrom capacitance fluctuations due to capacitance change 1603. Therefore,when a conductive surface comes within proximity of the capacitivesensor the capacitive sensor will sense the capacitanceC_(detection threshold) 1605, or some capacitance value aboveC_(detection threshold) 1605, such that the wear detection logic 1551 ofthe capacitance sensing and calibration logic 1550 will make adetermination that a conductive surface has been detected and is withinproximity of the capacitive sensor and therefore correspondingly is inproximity of the wearable device 1500. In some embodiments such as, butnot limited to, a wristwatch embodiment, the wearable device such as thewristwatch may be strapped tightly to the user's wrist. Under thesecircumstances, the capacitive sensor may detect a high capacitance valuesuch as C_(maximum) 1611 which would be an indication that the user hasthe wearable device attached tightly to the user's wrist.

Therefore as can be seen from the sensed capacitive graph 1600,conductive surface detection will occur within a conductive surfacedetection range 1609 which extends from a point above the baselinecapacitance C_(standalone) 1601, at C_(detection threshold) 1605, to themaximum capacitance C_(maximum) 1611. The detection thresholdC_(detection threshold) 1605 is used to limit the conductive surfacedetection range 1609 to begin above the “untouched” capacitanceC_(standalone) 1601 to avoid false detections due to changes in thecapacitance C_(standalone) 1601 which may occur due to capacitancechange 1603.

Another threshold C_(drift threshold) 1607 may also be established insome of the various embodiments. In such embodiments, capacitance valuesclose to C_(drift threshold) 1607, for example below C_(drift threshold)1607 down to the C_(standalone) 1601 or to C=0, may be considered tocorrespond to capacitances changes 1603 due to component drift such thatdrift compensation may be performed accordingly. Under circumstanceswhere the sensed capacitance is above C_(detection threshold) 1605, itis not possible to perform drift calibration or correction due to thehigh sensed capacitance values within the capacitance range 1609.However, values below C_(detection threshold) 1605 may not correspondexactly to an untouched state of the sensor. In other words, aconductive surface may still be in proximity although distant andtherefore barely sensed by the capacitive sensor. In such instances, itwould be useful to defer the drift compensation until it was more likelythat the capacitance change is due to the capacitance change 1603 due tocomponent drift. Therefore, the capacitance sensing and calibrationlogic 1552 decides accordingly when to perform drift calibration or not.The threshold C_(drift threshold) 1607 may therefore be used in someembodiments to provide further assurance that the sensed capacitancechanges are due to drift, in which case performance of drift calibrationis desirable. A high-level method of operation of the capacitancesensing and calibration logic 1550 is illustrated by the flowchart ofFIG. 17 which begins at block 1701.

It should be understood that the flowcharts of FIG. 17 and FIG. 18 showstart and end points for purpose of explaining the operations of thedescribed corresponding methods. However, these methods of operation maybe performed continuously while the capacitive sensor is operative, thatis, while the capacitive sensor is powered on which may correspond towhen the corresponding wearable device is powered on. The capacitanceand sensing logic is operative to perform the methods of operation,accordingly and in a continuous manner as appropriate. One method ofoperation begins a block 1701, and the capacitance sensing andcalibration logic 1550 monitors capacitance measured by a capacitivesensor. The capacitance sensing and calibration logic 1550 determines ifcomponent drift is measurable for components of the capacitive sensor asshown in decision block 1703. That is, the capacitance sensing andcalibration logic 1550 determines if the capacitance change observed bythe capacitive sensor 1517 is capacitance change 1603 (i.e. due tocomponent drift) or is due to a conductive surface being in proximity ofthe capacitive sensor 1517. For example, if the capacitive sensordetects a conductive surface based on sensing a capacitance value aboveC_(detection threshold) 1605, the capacitance sensing and calibrationlogic 1550 will defer drift calibration operations as shown in block1705. Drift calibration may be deferred in various ways such as, but notlimited to, deactivating the drift calibration logic 1553, or by placingthe drift calibration logic 1553 into a suspended mode or sleep mode orby imposing a wait state in which the drift calibration logic 1553 waitsfor further instructions, such as a wake-up or resume command, beforecommencing further activity. The process will then end as shown in block1709 because the capacitance change 1603 due to component drift cannotbe accurately measured. However, as long as the wearable device remainsin the “untouched” state, based on the capacitance value sensed by thecapacitive sensor 1517, the capacitance sensing and calibration logic1550 will perform drift calibration for the capacitive sensor as shownby operation block 1707. Put another way, capacitance values detected orsensed by the capacitive sensor that are within the conductive surfacedetection range 1609, which are above the non-touch capacitance valueC_(standalone) 1601 and meet the C_(detection threshold) 1605requirement, will result in a determination, by the wear detection logic1551 component, that the wearable device 1500 is being worn by the user.In such case, drift compensation cannot be performed properly and istherefore deferred. As noted above previously, the conductive surfacedetection range 1609 is dependent upon the actualC_(detection threshold) 1605 which may change based on such driftcalibration due to the capacitance change 1603. The capacitance change1603 may occur due to temperature variations or some other factors thatresult in changes in parasitic capacitance. Such capacitance changes1603 impact C_(standalone) 1601 and may occur over time as understood bythose of ordinary skill. The capacitance changes 1603 are taken intoaccount by the drift calibration operation performed in block 1707. Ifthe capacitive sensor remains untouched, such that the sensedcapacitance is equal to or near C_(standalone) 1601, then thecapacitance change 1603 can be measured and drift compensation can beperformed accordingly in process block 1707. In other words, thecapacitance sensing and calibration logic 1550 determines intervalsduring which drift compensation may be performed, or, on the other hand,looks for intervals during which drift compensation should be deferred.

As mentioned briefly above, a second threshold C_(drift threshold) 1607may be set, in some embodiments, such that the capacitance sensingcalibration logic 1550 makes a determination that the sensed capacitancevalue is within the capacitance change 1603 range and is due tocomponent drift and not due to proximity detection of a distantconductive surface. That is, for a sensed capacitance value within thecapacitance range 1603 near or below C_(drift threshold) 1607 and belowC_(detection threshold) 1605, the wear detection logic 1551 of thecapacitance sensing and calibration logic 1550 may send an activationsignal to the drift calibration logic 1553. In some instances when awristwatch wearable device or other wearable device is worn so looselythat it intermittently comes in contact with the user's wrist or bodysuch that the sensed capacitance remains below C_(drift threshold) 1607,the capacitance may be considered as being approximately equivalent tothe non-touch capacitance value C_(standalone) 1601 such that it ispossible to determine the capacitance change 1603 and make driftcalibration adjustments to the baseline capacitance. Therefore, in suchembodiments, any capacitance value within the capacitance range 1609would result in deferring the drift calibration operations of driftcalibration logic 1553.

Another scenario that may occur for wearable devices is that theconductive surface intermittently comes within contact or withinproximity of, the capacitive sensor such that the sensed capacitanceoscillates and is possibly sinusoidal such that the capacitance change1603 is also not able to be correctly determined. The flowchart of FIG.18 provides further details of operation and illustrates methods ofoperation that account for both intermittent detection and forcapacitance values within the capacitance range 1609 corresponding to aloosely worn device. The method of operation begins in block 1801 and aconductive surface may be detected as shown in decision block 1803. Ifsuch detection occurs in decision block 1803, then the calibrationsensing the capacitance sensing calibration logic 1550 determineswhether the capacitance value sensed is intermittent as shown indecision block 1805. If the capacitance values are intermittent, thendrift calibration is deferred as shown in block 1807. If no conductivesurface is detected in decision block 1803, then drift calibration maybe performed by the drift calibration logic 1553 as illustrated by thedrift calibration operation block 1811. The method of operation may thenend as shown in block 1809.

If the capacitance sensed by the capacitive sensor is not intermittentin decision block 1805, then the capacitance sensing calibration logic1550 will determine whether the sensed capacitance is withinC_(drift threshold) 1607 as shown in decision block 1813. If not, andfor example the capacitance sensed is within the capacitance range 1609,the drift calibration operation will be deferred as shown in block 1807and the process will end in block 1809. However if the capacitancesensed is within the threshold, for example if the capacitance sensed isbelow C_(drift threshold) 1607, drift calibration will be performed bythe drift calibration logic 1553 as shown in block 1815 and the processwill end in block 1809. The drift calibration operation of block 1811may be modified from the drift calibration operation of block 1815, ifsurface detection based on C_(detection threshold) 1605 is used totrigger or defer drift compensation. That is, if the verificationthreshold C_(drift threshold) 1607 is used in conjunction withC_(detection threshold) 1605, sensed capacitances may occur belowC_(detection threshold) 1605 that are not close enough to the non-touchcapacitance C_(standalone) 1601 to allow correct performance of driftcompensation. That is, the drift calibration logic 1553 may account forsome values of sensed capacitance below C_(detection threshold) 1605 andmay accordingly apply different adjustment values based on percentagechanges that are known or expected to be within a capacitance rangebetween 1605 and 1607. Otherwise, drift compensation is deferred untilthe sensed capacitance value is near or below C_(drift threshold) 1607,which is used to add further assurance that the sensed capacitance valueis within the capacitance change 1603 range and is due to componentdrift only (i.e. not due to a distant proximal conductive surface).

The flowchart of FIG. 19 describes methods of operation that provideadditional features and advantages when employing the capacitancesensing calibration logic 1550 in conjunction with a capacitive sensor.The method of operation begins in block 1901 and may run continuouslyprovided that the capacitive sensor is operative as shown in decisionblock 1902. For example, once the wearable device 1500 is powered up thecapacitive sensor may begin to be operative in that it begins to sensecapacitance changes as shown in decision block 1902. Whenever thewearable device 1500 is powered down the capacitive sensor may no longerbe operative in decision block 1902 and the method of operation of willterminate as shown in block 1915. Under some circumstances, and in someembodiments, the capacitive sensor may remain operative when thewearable device 1500 enters a sleep mode and when various otherprocesses and operations are shut down in order to conserve batterypower. Once the capacitive sensor is operative as shown in decisionblock 1902, the capacitive sensor monitors capacitance and thecapacitance sensing and calibration logic 1550 waits for changes incapacitance as shown in input block 1903. When any capacitance change issensed by the capacitive sensor in decision block 1905, thedetermination of whether the sensed capacitance is above the detectionthreshold is made in decision block 1907. For example, if the capacitivesensor detects a capacitance above C_(detection threshold) 1605, weardetection logic 1551 of the capacitance sensing calibration logic 1550,may conclude that the wearable device 1500 is being worn as shown inblock 1909. In response to this conclusion, the calibration sensing thecapacitance sensing calibration logic 1550 may interact with variouscomponents of the wearable device 1500 including software such asapplications 1511. Some of the components of wearable device 1500,including applications 1511, may benefit from an indication that thewearable device 1500 is being worn by the user or is otherwise in use.For various reasons such as, but not limited to, conservation of batterycharge, some processes or applications 1511 may be deferred fromoperation until the wear detection logic 1551 determines that thewearable device 1500 is in use. Such “in use” processes or applicationsmay be initiated in process block 1911 accordingly as shown and driftcalibration will be deferred in block 1913. In addition, the capacitancesensing calibration logic 1550 will determine whether the sensedcapacitance is changing intermittently as shown in decision block 1917.If yes, intermittent capacitance detection in decision block 1917 mayinitiate motion detection logic 1555 which may receive information fromthe wear detection logic 1551 component, or may receive input directlyfrom the capacitive sensor, i.e. by way of the connection bus 1505. Themotion detection logic 1555 may provide outputs to various components ofwearable device 1500 or to one or more applications 1511. The motiondetection logic 1555 may also send command and control signals to placevarious components of the wearable device 1500 into a low power or sleepmode in order to conserve battery power. For example, based on thedetection of motion and for given “levels” or motion detected by themotion detection logic 1555, the display/UI 1513 may be turned off untilthe motion stops so as to conserve power, since it is unlikely thedisplay will be useful if the detected motion indicates that the usermay be in continuous motion such as when running.

Some processes or applications may be desirable to operate when thewearable device 1500 is determined to be in motion. Therefore, based onthe capacitance changing intermittently in decision block 1917 anyprocesses or applications 1511 which are “in motion” processes may beinitiated as shown in process block 1919. For example, the motiondetection logic 1555 may provide outputs to drive a pedometerapplication, a sleep monitor application of some other application orprocess, etc., that require the user to be in motion in order toproperly function or to receive information. Provided the capacitivesensor is still operative as shown in decision block 1902, thecapacitive sensing and calibration logic 1550 will continue to wait forcapacitance changes as shown in input block 1903 and the method ofoperation will continue.

If the sensed capacitance was above the detection threshold in decisionblock 1907, and is not changing intermittently in decision block 1917,drift calibration operations would still be deferred as shown in block1913 and capacitance sensing and calibration logic 1550 would continueto wait for input in block 1903. However, as was discussed above withrespect to sensed capacitance graph 1600, a second threshold,C_(drift threshold) 1607, may be established by the capacitance sensingand calibration logic 1550. In this example, decision block 1923 andblock 1925 which, as indicated by dotted lines in FIG. 19, are not usedin all embodiments, may be implemented. In this example scenario, if thesensed capacitance is within the second threshold C_(drift threshold)1607, such as below it, in decision block 1923, then drift calibrationwill be performed in block 1921. However, if the C_(drift) threshold1607 is not met, then drift calibration will still be deferred in block1925 due to uncertainty as to whether the capacitance sensed is due todrift or due to a distant proximal conductive surface being detectedbelow the C_(detection threshold) 1605. In embodiments where theC_(drift threshold) 1607 is not used, drift calibration is performed inblock 1921 for any sensed capacitance below C_(detection threshold) 1605in decision block 1907.

Returning to decision block 1905, in some embodiments if the sensedcapacitance is not above the detection threshold in block 1907, thecapacitance calibration and sensing logic 1550 looks for changes incapacitance in decision block 1923 that meet the C_(drift) threshold1607 and then the drift calibration logic 1553 will perform driftcalibration in block 1921 and the process may continue. Otherwise, driftcalibration is deferred in block 1925 and the process continues as shownand capacitance continues to be monitored.

Turning to FIG. 20, a partial schematic block diagram of a capacitivesensor 1301 as shown in FIG. 13 (or 1401, 1433, 1443 in FIG. 14 or 1517,1533, 1543 in FIG. 15) and in accordance with various embodiments willnow be described. As discussed above with respect to FIG. 2, FIG. 3 andFIGS. 7A, 7B and 7C, a wearable device in accordance with someembodiments has a housing which is an enclosure that has a first portionand a second portion, where one of the first portion or the secondportion may be considered to be a cover of the housing or enclosure.Thus, a sensor conductor 2005 may be located on a PCB surface as shownin FIG. 7A, 7B or 7C, or may be a section of a housing portion, such asa cover, as shown in FIG. 4. The first housing portion has at least oneconductive section 2009 that is connected to circuit ground 2011 by aconnection 2013.

A power source provides a voltage V_(DD) 2001 to power capacitive sensorcircuitry 2000. The power source may be a rechargeable battery, adisposable battery, a solar battery, a battery that is recharged byelectrostatic or gyroscopic energy or wireless recharging, etc. Thecapacitive sensor circuitry 2000 includes at least one oscillator 2003and may include other “capacitive sensor components” such as, but notlimited to, comparators, clocking circuits, operational amplifiers,other active components such as transistors, and passive components,etc. The capacitive sensor circuitry 2000 is operatively coupled to thecapacitance sensing and calibration logic 1320 by connection path 1303,and is connected to circuit ground 2011 by connection 2015. Thecapacitive sensor circuitry 2000 is connected to the sensor conductor2005 by connection 2007 and drives the voltage to provide a charge onthe sensor conductor 2005. That is, the sensor conductor 2005 forms one“plate” of a capacitor and the grounded conductive section 2009 of thehousing portion forms the other capacitor “plate.”

As a conductive surface comes within proximity of the sensor conductor2005 and grounded conductive section 2009, the electric field isdisrupted and the variable capacitances Cs and Cg change to impact theoverall capacitance value viewed by the capacitive sensor circuitry2000. The node 2017 represents the point where the conductive surface(such as the user's wrist, etc.) comes into proximity or contact andforms the capacitances Cs and Cg. Cs represents the capacitance formedbetween the conductive surface and the sensor conductor 2005. An exampleis when the user's wrist, which in this case is the conductive surface,comes within proximity of the sensor conductor 2005. The user's bodyalso creates a variable capacitance Cg between the user's body andground by being in proximity to the grounded conductive section 2009 asillustrated by node 2017. The capacitance Csg represents the capacitancethat exists between the sensor conductor 2005 and the groundedconductive section 2009 including any parasitic capacitance that mayexist as was described above with respect to the various structures thatmay be utilized. The capacitive sensor circuitry 2000 sees a totalcapacitance which is determined by the parallel combination of Cs and Cgin series, with Csg. That is, the capacitance computation for the totalcapacitance seen by the capacitive sensor circuitry 2000=Ceq=[(Cs and Cgin series)+Cg]=[(CsCg)/(Cs+Cg)]+Cg. An equivalent resistance value R isalso seen between the “plates,” and in some embodiments, a driven shield2019 may be operatively coupled 2021 by the operational amplifier 2023,both of which are shown in dotted lines to illustrate that they may, ormay not, be present in any particular embodiment. The driven shield 2019is a PCB layer as discussed, for example, with respect to FIG. 6, FIG.7C and FIG. 8. The driven shield 2019 protects any other circuitry,components, etc. from undesired coupling or interference due to thesensor conductor 2005 and/or the conductive section 2009.

The capacitive sensor circuitry 2000 may be implemented in various waysin the various embodiments such as by discrete components, integratedcircuits, etc. as was discussed above with respect to the capacitancesensing and calibration logic 1320. The capacitive sensor circuitry 2000may be implemented on one or more layers of the PCB having the sensorconductor 2005 or on a different PCB positioned within the housing. Thecapacitive sensor circuitry 2000 may be integrated, in whole or in part,with the capacitance sensing and calibration logic 1320 as was discussedpreviously above.

While various embodiments have been illustrated and described, it is tobe understood that the invention is not so limited. Numerousmodifications, changes, variations, substitutions and equivalents willoccur to those skilled in the art without departing from the scope ofthe present invention as defined by the appended claims.

What is claimed is:
 1. A method comprising: responsive to determining,by a wearable computing device, that a capacitance sensed by acapacitive sensor of the wearable computing device is intermittentlyabove a detection threshold: determining, by the wearable computingdevice, that component drift for the capacitive sensor cannot bedetermined, wherein a capacitance value above the detection thresholdindicates that a conductive surface is within a proximal distance of thecapacitive sensor; and while the capacitive sensor intermittently sensesthe capacitance above the detection threshold, deferring a driftcalibration operation for the capacitive sensor.
 2. The method of claim1, further comprising: determining, by the wearable computing device,based on sensed intermittent changes in the capacitance, that thewearable computing device is in motion.
 3. The method of claim 2,further comprising: responsive to determining, by the wearable computingdevice, that the capacitance sensed by the capacitive sensor meets asecond threshold below the detection threshold, performing the driftcalibration operation for the capacitive sensor.
 4. The method of claim2, further comprising: responsive to determining that the wearabledevice is in motion, providing a control signal to a component or anapplication of the wearable device.
 5. The method of claim 1, furthercomprising: responsive to determining, by the wearable computing device,that the capacitance is below the detection threshold intermittently fora period of time, performing the drift calibration operation for thecapacitive sensor.
 6. The method of claim 1, further comprising:responsive to determining, by the wearable device, based on thecapacitance sensed by the capacitive sensor, that the wearable computingdevice is in use, providing a control signal to a component or anapplication of the wearable computing device.
 7. A wearable devicecomprising: a capacitive sensor; and capacitance sensing and calibrationlogic operatively coupled to the capacitive sensor, the capacitancesensing and calibration logic operative to, responsive to determiningthat a capacitance sensed by the capacitive sensor is intermittentlyabove a detection threshold: determine that component drift for thecapacitive sensor cannot be determined, wherein a capacitance valueabove the detection threshold indicates that a conductive surface iswithin a proximal distance of the capacitive sensor; and while thecapacitive sensor intermittently senses the capacitance above thedetection threshold, deactivate a drift calibration operation for thecapacitive sensor.
 8. The wearable device of claim 7, wherein thecapacitance sensing and calibration logic is further operative to:determine, based on sensed intermittent changes in the capacitance, thatthe wearable device is in motion.
 9. The wearable device of claim 8,wherein the capacitance sensing and calibration logic is furtheroperative to: responsive to determining that the capacitance sensed bythe capacitive sensor meets a second threshold below the detectionthreshold, perform the drift calibration operation for the capacitivesensor.
 10. The wearable device of claim 7, wherein the capacitancesensing and calibration logic is further operative to: responsive todetermining that the capacitance is below the detection thresholdintermittently for a period of time, perform the drift calibrationoperation for the capacitive sensor.
 11. The wearable device of claim 8,wherein the capacitance sensing and calibration logic is furtheroperative to: responsive to determining that the device is in motion,provide a control signal to a component or an application of thewearable device.
 12. The wearable device of claim 7, wherein thecapacitance sensing and calibration logic is further operative to:responsive to determining, based on the capacitance sensed by thecapacitive sensor, that the wearable device is in use, provide a controlsignal to a component or an application of the wearable device.